yeah, you are correct to a certain extent. i believe thats why he is a solo artist. Recent albums have had him singing some songs, and i agree that in a band, with lyrics etc...Vai isnt as strong as others. You add his Sex & Religion album from back in 1993 to that, even though i thought it was still good, and it backs up the statement.
But Vai's strengths are solo albums, and i believe that no one can really rival him in that department.
but then again, its different strokes for different folks. Thats the beauty about music, its how it grabs your emotions. Ones emoitions differ to another.